In the past, attempts have been made to provide a process for reclaiming used or spent motor oils obtained, for example, as the drainings from the crankcases of automobiles or trucks.
The most widely used process today for reclaiming spent motor oil involves, as an initial step, flashing the gasoline or diesel oil content which might be present in the oil. This step is followed by treating the oil with a large amount, i.e. about 10-15% by volume of concentrated (.about.98%) sulfuric acid thereby forming suplhonic acid derivatives of the petroleum hydrocarbons. The result of this treatment is to convert about 50% of the feed to oil-insoluble sulphonic acids that form an acid sludge referred to in the art as "green acid". This material must be discarded.
The portion of the treated feed remaining after separation from the sludge and extraction with clay is comprised of oil-soluble sulphonic acids. The clay extractant, however, is usually discarded or reactivated where feasible.
Another effect of treating the spent motor oil with the large volumes of sulfuric acid used in the prior art process is the destruction of the viscosity index improvers used in most modern motor oil formulations. These materials, referred to as V.I. improvers, are typically relatively low molecular weight polyisobutylene or polymethylmethacrylate.
Approximately half the motor oil today is so-called multi-viscosity oil, for example the commonly available SAE 10W-30 weight or 10W-40 weight oils sold in service stations. Such oils are made by formulation of a refined light neutral oil having a viscosity in the range of 90-130 SSU/100.degree. F. and 10-40% of the viscosity improvers referred to above.
Since the previously employed reclaiming process destroys the V.I. improvers, the reclaimed oil has a viscosity rating of about 20 SAE. This viscosity is too low for use as motor oil without reformation with V.I. improvers.
From the preceding discussion, it should be apparent that the prior art process of reclaiming oil involving treating it with 10-15% or more by volume of sulfuric acid is attended by serious disadvantages in that half of the spent oil feed is converted to a useless product and the viscosity improving additives are destroyed. Nevertheless, the use of this large volume of acid is required in the process in order to neutralize or destroy certain dispersant additives, principally the ashless detergent, a diester of succinic acid, used in many modern motor oils to keep particles, for example, particulate carbon, suspended in the oil during its lifetime in the crankcase. Destruction or neutralization of these additives causes the suspended particles to precipitate making their removal a convenient process.
Some of the problems associated with the process described supra are avoided by employing a more recently developed process. This process requires a vacuum distillation of the spent oil. By this technique, a light oil distillate is obtained that can be reused in motor oil. However, the bottoms in the distallation contain the polymeric V.I. improvers as well as those impurities which it is desired to remove. As a result, the distillate must be reformulated with a V.I. improver if it is to be used as a motor oil.
The limitations of the prior art processes have resulted in a situation wherein reclaimed motor oil as a blending stock to be used in the manufacture of motor oil is not an economically viable alternative to the use of virgin stock obtained as a product of refining petroleum. Therefore, there has been little economic incentive to provide facilities for collecting and reclaiming crankcase drainings. Disposal of the large quantity of this material has a significant negative impact on the environment and measurably increases the amount of petroleum that is consumed each year.
Accordingly, it is an object of this invention to provide an improved process for reclaiming spent motor oil.
Yet another object of this invention is to provide an improved stock for formulating motor oil derived from spent motor oil.
The achievement of these and other objects will be apparent to those skilled in the art when the following descriptions of the invention is considered.